1. Field of the Invention
The present invention relates to a method and composition for preserving the surfaces of aluminium, and particularly the surfaces of anodized aluminium.
2. Description of Related Art
Despite the well known resistance to corrosion of aluminium and more particularly, electrolytically oxidized aluminium, it is recognized that aluminium components which are exposed to external weathering or to aggressive media should additionally be protected by a preserving coating.
Thus, it is proposed in U.S. Pat. No. 4,465,562 to immerse aluminium which has been anodically oxidized, but not surface-sealed, in an acidic polymer latex which irreversibly deposits a polymer layer on the surface of the aluminium. The disadvantages of this process lie in the fact that it can only be applied immediately after the anodic oxidation step and that the articles thus coated do not have the surface quality obtained by controlled, uniform sealing of the anodically produced oxide layer.
Another process for preserving aluminium surfaces is described in German Pat. No. 3,024,727 which proposes using a metal salt-containing dispersion containing 10 to 25% by weight of acrylate copolymers in fully deionized water as a preservative for electrolytically oxidized aluminium surfaces. However, this German Patent contains only a broad, vague technical teaching which does not enable one skilled in the art to preserve aluminium components by a uniform, streak-free coating without inventive activity. Nor is there any disclosure in the above German Patent to immersion treatment, which is a particularly desirable method of carrying out such surface sealing of aluminium.